Date of Award
Doctor of Philosophy
Ecology, Evolution, and Organismal Biology
Ecology and Evolutionary Biology
Carol M. Vleck
Most current knowledge of the effects of age on immune function comes from studies in humans, laboratory models, and domesticated animals. This dissertation explored variation in immune function in relation to age in free-living animals by investigating patterns, mechanisms and their implications in tree swallows, a widespread passerine species in North America. The first study investigated the ontogeny of immune defense in tree swallows and found some support for the prediction that innate immune defenses should reach adult levels earlier than adaptive defenses, but limited support for the prediction that adaptive defenses would be more related to body condition than innate defenses. Overall, immune function of the young is poorly developed compared to that of adults, as is the case for humans and laboratory or domesticated animals. The second study focused on the opposite extreme of the lifespan investigating the aging of the immune system in tree swallows. This study shows that not all components of immune function are equally affected by age and provides the most thorough description of immunosenescence patterns and mechanisms in a free-living vertebrate population to date. Overall, aspects of T-cell function seem to be the most affected by age in tree swallows, as is known for humans and laboratory animals. Having documented the pattern of immunosenescence, the third study investigated the consequences of immunosenescence in free-living tree swallows through a field experiment simulating a bacterial infection (challenge with lipopolysaccharide, LPS) in females of different ages during the nestling rearing period. This study provided support for the hypothesis that older, immunosenescent individuals pay higher costs than younger ones when faced with a challenge to their immune system and that these costs are mediated by an exaggerated sickness behavior, as seen in laboratory rodents. These results provided the first evidence of costs of immunosenescence in free-living animals. Finally, the fourth study investigated the relationships among six measures of immune defense commonly used in ecoimmunology studies that were assessed simultaneously in individual free-living tree swallows. This study identified three main axes of variation in immune function among individuals, representing variation in T-cell function, B-cell function, and innate immune function. A trade-off within the acquired arm of the immune system was apparent only when controlling for variation in body condition, age, and general quality among individuals. This study also highlighted that classification of some immune components as innate or acquired is ambiguous and as such can lead to ambiguous interpretation of results, if this is not acknowledged. Overall, this dissertation provides the most thorough description of ontogeny and senescence patterns of immune function in any free-living animal to date and shows that age is an important factor influencing immune responses in the wild.
Maria Gabriela Palacios
Palacios, Maria Gabriela, "Effects of age on immune function in free-living animals: Ontogeny, senescence, and their implications" (2009). Graduate Theses and Dissertations. 10912.